Could Renewable Energy Be Stored in Balloons in the Ocean?

Just short of two miles off the coast of Toronto, a series of six massive, cylindrical balloons rise from the ocean floor, standing almost as tall as a two-story house. Their walls contain compressed air with the potential to become electricity.

These balloons are part of an innovative, emissions-free scheme to store renewable energy from the company Hydrostor.

You see, wind energy is wonderful and solar panels are superb, and these technologies becomes more efficient every year. Yet, one of the biggest challenges for renewable energy is powering homes during off-peak times, once the winds die or after the sun sets, when communities often turn towards burning diesel.

Hydrostor is one of several companies and research groups who are investigating Underwater Compressed Air Energy Storage (UW-CAES), which could be a low-cost and environmentally-friendly answer to this problem.

In Hydrostor’s system, excess energy from solar or wind charges an air compressor. The compressed air is cooled before it shoots down a tube and out to the massive balloons. Just like blowing up a balloon on land, the air fills up the balloons in the ocean, but because of the many feet of water pushing down, the air inside compresses. The deeper the balloons, the more air they can hold. To release the energy, operators can open an onshore valve and the overlying water forces the air out, which spins a turbine to generate power.

“Ultimately we are a very cool underwater air battery,” Cameron Lewis, founder and president of Hydrostor, says in a video released about the project.

CAES isn’t exactly new. The technology has been around since the late 19th century, though it wasn’t until the late 1970s that the first energy storage plant opened in Bremen, Germany, with compressed air underground locked in old salt caverns. Since then, there have been several CAES projects around the world, but the problem always comes down to where you put the air, says VanWalleghem. Steel tanks are extremely expensive and the current low-cost alternatives—underground caverns—are never where you need them, he says. Hydrostor’s underwater balloons could at least make the energy storage method possible in communities near the ocean or deep lakes.

Sitting under roughly 180 feet of water, Hydrostor’s six test balloons measure 29.5 feet tall and 16.4 feet wide. They are made of a urethane-coated nylon, which is the same material used to haul shipwrecks from lake and sea floors—a fabric that can withstand a good deal of force from air deep underwater.

Hydrostor isn’t the only company investigating UW-CAES. Thin Red Line Aerospace independently developed a similar system, and in 2011 and 2012, they deployed several “Energy Bags” off the coast of Scotland’s Orkney islands for three months. This initial pilot test gave encouraging results, which they published in a study in collaboration with a team from the University of Nottingham.

“The challenge is a step to grid scale,” says Thin Red Line’s founder and president Max de Jong. Or rather, figuring out how to store enough air to produce a significant amount of energy.